Remote sensing or hyper-spectral imaging often uses the sun for illumination, and the short-wave infrared (SWIR) windows of about 1.5-1.8 microns and about 2-2.5 microns may be attractive because the atmosphere transmits in these wavelength ranges. Although the sun can be a bright and stable light source, its illumination may be affected by the time-of-day variations in the sun angle as well as weather conditions. For example, the sun may be advantageously used for applications such as hyper-spectral imaging only between about 9 am to 3 pm, and it may be difficult to use the sun during cloudy days or during inclement weather. In one embodiment, the hyper-spectral sensors measure the reflected solar signal at hundreds (e.g., 100 to 200+) contiguous and narrow wavelength bands (e.g., bandwidth between 5 nm and 10 nm). Hyper-spectral images may provide spectral information to identify and distinguish between spectrally similar materials, providing the ability to make proper distinctions among materials with only subtle signature differences. In the SWIR wavelength range, numerous gases, liquids and solids have unique chemical signatures, particularly materials comprising hydro-carbon bonds, O—H bonds, N—H bonds, etc. Therefore, spectroscopy in the SWIR may be attractive for stand-off or remote sensing of materials based on their chemical signature, which may complement other imaging information.
A SWIR super-continuum (SC) source may be able to replace at least in part the sun as an illumination source for active remote sensing, spectroscopy, or hyper-spectral imaging. In one embodiment, reflected light spectroscopy may be implemented using the SWIR light source, where the spectral reflectance can be the ratio of reflected energy to incident energy as a function of wavelength. Reflectance varies with wavelength for most materials because energy at certain wavelengths may be scattered or absorbed to different degrees. Using a SWIR light source may permit 24/7 detection of solids, liquids, or gases based on their chemical signatures. As an example, natural gas leak detection and exploration may require the detection of methane and ethane, whose primary constituents include hydro-carbons. In the SWIR, for instance, methane and ethane exhibit various overtone and combination bands for vibrational and rotational resonances of hydro-carbons. In one embodiment, diffuse reflection spectroscopy or absorption spectroscopy may be used to detect the presence of natural gas. The detection system may include a gas filter correlation radiometer, in a particular embodiment. Also, one embodiment of the SWIR light source may be an all-fiber integrated SWIR SC source, which leverages the mature technologies from the telecommunications and fiber optics industry. Beyond natural gas, active remote sensing in the SWIR may also be used to identify other materials such as vegetation, greenhouse gases or environmental pollutants, soils and rocks, plastics, illicit drugs, counterfeit drugs, firearms and explosives, paints, and various building materials.
In one embodiment, a measurement system comprises a light source configured to generate an output optical beam, the light source comprising one or more semiconductor sources configured to generate an input beam, one or more optical amplifiers configured to receive at least a portion of the input beam and to deliver an intermediate beam to an output end of the one or more optical amplifiers, one or more optical fibers configured to receive at least a portion of the intermediate beam and to deliver at least the portion of the intermediate beam to a distal end of the one or more optical fibers to form a first optical beam, a nonlinear element configured to receive at least a portion of the first optical beam and to broaden a spectrum associated with the at least a portion of the first optical beam to at least 10 nm through a nonlinear effect in the nonlinear element to form the output optical beam with an output beam broadened spectrum, wherein at least a portion of the output beam broadened spectrum comprises a near-infrared wavelength between approximately 700 nanometers and approximately 2500 nanometers, and wherein at least a portion of the one or more fibers is a fused silica fiber with a core diameter less than approximately 400 microns. The system also includes a measurement apparatus configured to receive a received portion of the output optical beam and to deliver a delivered portion of the output optical beam to a sample, wherein the delivered portion of the output optical beam is configured to generate a spectroscopy output beam from the sample, and a receiver configured to receive at least a portion of the spectroscopy output beam having a bandwidth of at least 10 nanometers and to process the at least a portion of the spectroscopy output beam to generate an output signal, wherein the light source and the receiver are remote from the sample, and wherein the sample comprises plastics or food industry goods.
In another embodiment, a measurement system comprises a light source configured to generate an output optical beam, the light source comprising a plurality of semiconductor sources configured to generate an input optical beam, a multiplexer configured to receive at least a portion of the input optical beam and to form an intermediate optical beam, one or more fibers configured to receive at least a portion of the intermediate optical beam and to form the output optical beam, wherein at least a portion of the one or more fibers comprises a fused silica fiber having a core diameter less than approximately 400 microns, wherein the output optical beam comprises one or more optical wavelengths, at least a portion of which are between approximately 700 nanometers and approximately 2500 nanometers, and wherein the output optical beam has a bandwidth of at least 10 nanometers. The system includes a measurement apparatus configured to receive a received portion of the output optical beam and to deliver a delivered portion of the output optical beam to a sample, wherein the delivered portion of the output optical beam is configured to generate a spectroscopy output beam from the sample, and a receiver configured to receive at least a portion of the spectroscopy output beam having a bandwidth of at least 10 nanometers and to process the at least a portion of the spectroscopy output beam to generate an output signal, wherein the light source and the receiver are remote from the sample, and wherein the sample comprises plastics or food industry goods.
In another embodiment, a method of measuring comprises generating an output optical beam comprising generating an input optical beam from a plurality of semiconductor sources, multiplexing at least a portion of the input optical beam and forming an intermediate optical beam, guiding at least a portion of the intermediate optical beam using one or more fibers including a fused silica fiber having a core diameter less than 400 microns, and broadening a spectrum of at least a portion of the intermediate optical beam to at least 10 nanometers to form the output optical beam with an output beam broadened spectrum, wherein the output optical beam comprises one or more optical wavelengths between 700 nanometers and 2500 nanometers. The method also includes receiving a received portion of the output optical beam and delivering a delivered portion of the output optical beam to a sample comprising plastics or food industry goods located remotely from the generated output optical beam, generating a spectroscopy output beam having a bandwidth of at least 10 nanometers from the sample, wherein the spectroscopy output beam comprises spectral features of hydrocarbons or organic compounds, receiving at least a portion of the spectroscopy output beam, and processing the at least a portion of the spectroscopy output beam and generating an output signal.